Method of grinding screw threads in shouldered work



I I a I Inventor? a\ a\ a a. a g; $2 j J l I I 1 Nov. 2, 1937. J. HARLEY I METHOD OF GRINDING SCREW THREADS IN SHOULDERED WORK Filed NOV. 21, 1935 Q Egg Aftorney.

Patented Nov. 2, 1937 UNITED STATES PATENT OFFICE 2,098,145 rm'rnon or on'mnmo scnnw 'rnnnsn 1N SHOU LDEBED WORK smiley Jaifa nal-icy, Stivichall, amt... manna Application November 21, 1935, Serial No. 50,949

- In Great 10 ed surfaces on shouldered work without frequenttrueing of the wheel.

The methodadopted according to this invention consists in causing a plurality of spaced grinding surfaces, each having a series of peripheral annular thread-form serrations,to operate in succession upon the work with relative axial movement, and in causing'relative radial movement to take place between the work and said surfaces between successive operations to enable.

80 the first surface, after rough-grinding the thread ,-up to the shoulder on .the work, to clear said shoulder, and at the same time to enable the next surface to come into operation on the work to remove inaccuracies in the thread at the shoul- 25 der caused by wear of the leading serrations of the first grinding surface.

v An economic advantage of the adoption of the improved method occurs where a number of members are required to be similarLv ground.

In such cases the grinding surfaces operate successively on each member in such a manner that while one member is being operated on by one grinding surface another member previously operated on by the latter is being operated on at the same time by another. grinding surface. In this way the complete grinding operation can be carried on continuously along a series of co- ,axially arranged work-pieces each of which can be successively rough ground by onegrinding surface and finish ground by another of the grinding surfaces.

The improved method involves the .use of either a single grinding wheel having two or more axially discontinuous peripheral grinding surfaces or a plurality of grindingwheels arranged eo-axially 'or otherwise and spaced'apart from each other. In each case the several grinding surfaces may be of the same or of different 50 diameters and can have different abrasive qualities.

The invention will be hereinafter described by way of example to the production and finishing of threaded work by means of grinding surfaces 55 each having a plurality of annular serrationsor Britain November 26, 1934 2 Claims. (Cl. 51-278) cutting edges, reference being made to the accompanying drawing, wherein,

Figures 1 and 2 illustrate the use of a multiple grinding wheel in grinding shouldered work in accordance with the present invention. 5 Figures 3, 4 and 5 illustrate alternative forms of grinding wheel which can be employed in carrying out the improved method of grinding threaded members. 1

Figure 6 illustrates the application of the imill proved method to the grinding of a co axially arranged series of similar members.

Owing to the fact that a grinding wheel tends to wear taper at the leading edge it is difilcult with. a single wheel to produce or to finish a l5 screw thread which shall be uniformly accurate up to a shoulder, without frequent re-dressing of the wheel and repeated traversing of the work in operative contact therewith.

This diiiiculty is to 'a very large extent removed and the grinding operation very considerably facilitated by the use of multiple or compound grinding wheels of the kind, and in the manner hereinafter described with reference to the drawing. I Where it is desired to produce a screw thread on a piece of shouldered work, such'as the valve seat it represented in Figures 1 and 2, a pair of grinding wheels I), 17 arranged in tandem are employed. The said wheels rotate together about a common axis and are spaced apart a distance exceeding the overall axial length of the work including the shoulder a thereon. In this case the wheels are shown as being of the same nominal diameter and are each formed with a plural-' ity of annular serrations or cutting edges correspending with the thread to be ground in the work. The work is mounted between centres c,

c and adapted to be slowly rotated in successive contact with the rapidly rotating grinding 40 wheels b. b

In order to bring the grinding surfaces of the wheels into successive operation on the work it is necessary, in addition to the feed, to provide' for relative movement between the latter and the wheels. For this purpose the grinding wheels may be carried by a head (not. shown) arranged tohave radial and .axial movements in relation to the'work piece, or vice versa or,

alternatively, one of these two movements can be given tothe head and the other to the workcarrien. The two movements may be performedin any well known manner For example, the

grinding wheel ;head or the work-carrier, as the case'may be, may be mounted upon a slide sub- 68 sufilcient to clear the shoulder on the work and.

to shift the grinding wheel head or the workcarrier in an axial direction to a position in which the other of said wheels can be brought into operation on the work, as seen in Figure 2.

For the axial movement at the termination of the first grinding operation it may be arranged for the traversing movement of the work to be temporarily accelerated after the first wheel b has been withdrawn from the work to clear the shoulder thereon, after which the normal traversing movement will be resumed whilst the second wheel b is in operation on the work. The advantage of using two grinding wheels in tandem is that the oversize threads left near the shoulder during the rough grinding operation of thefirst wheel b can be reduced tothe correct size by the succeeding finish grinding operation of the second wheel b Whether the grinding wheels are made separately and secured together between flanges with a distance piece d between them as shown in Figures 1, 2 and 3, or a single wheel is used having spaced grinding surfaces b, b as shown in Figures 4 and 5, the said wheels or surfaces may be of the same (Figures 1, 2, 4 and 6) or of difi'erent diameters, (Figures 3 and 5).

For trueing purposes it is an advantage to use wheels or surfaces of equal diameters, but for grinding work having a long shouldered portion it is an advantage to use a finishing wheel or surface of larger diameter than that of the rough grinding wheel or surface.

Where a number of shouldered work-pieces a .are required to be similarly threaded an economy in the grinding operation is obtained by mounting them in co-axlal series, as shown in Figure 6, and operating on them in succession by means of a multiple or compound grinding wheel b, b of either of the kinds above described. By means of this arrangement a number of parts can be screw threaded in considerably less time than would be taken up in threading them separately, because after the first of the series has been rough ground by the wheel b both grinding wheels or surfaces are in operation at the same time, that is to say, while first wheel b is rough grinding a thread on one part a the second wheel b is finish grinding the previously rough ground thread on another part a.

The serrated or ribbed periphery of each grinding-wheel or surface may, if desired, be formed with a backward taper, i. c. with the leading edge having the greatest diameter so that as the wheel wears new serrations or ribs come successively into active operation on the work thereby prolonging the useful life between dressings.

0f the wheel.

For certain purposes it may be advantageous to arrange one or more of the successively operating grinding wheels at each side of the work carrier in which case they need not necessarily be arranged co-axial with each other.

The abrasive qualities of the several grinding surfaces need not necessarily be of the same grit, it may be advantageous in some cases to use hard and soft wheels in combination.

I claim:--

1. The method of grinding screw threads in shouldered work which consists in causing a roughing in grinding surface and a finishing grinding surfaceto rotate as a unit, causing said roughing in grinding surface to engage the face of the work, causing relative axial movement between the work and said roughing in surface during the entire operation of said roughing in surface upon the work, causing relative radial movement between the grinding surfaces and the work when the roughing-in operation of the work has been completed to clear the shoulder on the work, causing the finishing grinding surface to operatively engage the work after the roughing-in grinding operation has been completed, and finally causing relative axial movement between the work and the finishing grinding surface during the entire operation of the latter upon the former.

2. The method of grinding screw threads in a plurality of shouldered work pieces which consists in causing a roughing in grinding surface and a finishing grinding surface to rotate as a unit, causing said surfaces to operate simultaneously on two work pieces to rough-in the screw-threads on one work piece and to finish the screw-threads previously roughed-in on the other work piece, causing relative axial movement between said grinding surfaces and said work pieces respectively during the entire grinding operation, causing relative radial moy ement between said grinding surfaces and said work pieces after said grinding operations have been completed, causing relative radial and axial movement between said grinding surfaces and between said work pieces and a third work piece whereby the work piece Just ground by the finishing grinding surface will not be further operated upon, the work piece just roughed-in will be so related to the finishing surface as to be operated -on thereby and the third work piece will be so related to the roughing-in grinding surface as to be operated on thereby, causing relative radial movement between said grinding surfaces and the previously roughed-in work piece and the third work piece respectively to cause the finishing grinding surface to operate on the previously roughed-in work piece and the roughingin grinding surface to operate on the third work piece, and causing relative axial movement between said grinding surfaces and said work pieces during 'this entire grinding operation.

STANLEY JAFFA HARLEY. 

